It depends, if you try to taunt kill him and then you fail and end up dead then that would be your enemy. On the other hand, if you kill him while he's laughing then he would have laughed before his demise thus making it his "last laugh". Of course if another player on the enemy team killed you while laughing, then perhaps, it would be you who face their " last laugh" (until you respawn that is*).

It depends, if you try to taunt kill him and then you fail and end up dead then that would be your enemy. On the other hand, if you kill him while he's laughing then he would have laughed before his demise thus making it his "last laugh". Of course if another player on the enemy team killed you while laughing, then perhaps, it would be you who face their " last laugh" (until you respawn that is*).

*excluding arena mode

So in other words, it’s a temporal paradox that has engulfed both factions that will continually force this same event till the end of time. Or till the server crashes, admin bans the heavy’s for being useless or someone remembers they have a gun..